Making sense of Greenland’s ice

A widely publicised paper in Science last week discussed the recovery ancient DNA from the base of the Dye-3 ice core (in southern Greenland). This was an impressive technical feat and the DNA recovered may well be the oldest pure DNA ever, dating back maybe half a million years. However much of the press coverage of this paper dwelt not on the positive aspects of the study but on its supposed implications for the stability of the Greenland ice sheet and future sea level rise, something that was not greatly discussed in the paper at all. So why was this?
As we have seen before, the frame for most media reports are set by the press release, and in this case, the press release from the Wellcome Trust (jointly issued by NERC) entitled “Greenland’s ancient forests shed light on stability of ice sheet”. This contained the quote “… this means that the southern Greenland ice cap is more stable than previously thought.” from the lead author Professor Willerslev which ended up being the peg for many of the stories. This quote did not appear in simultaneous releases from AAAS, University of York or the University of Alberta, which were much closer to the text of the paper.

The context for these statements is the uncertainty associated with the history of the Greenland ice sheet – particularly what happened during the last interglacial period (also sometimes called the Eemian) around 125,000 years ago – a time when the orbital configuration lead to Northern Hemisphere summer temperatures being perhaps 1 or 2 deg C warmer than today (and 3 to 5 degrees warmer around Greenland). It is uncontroversial that sea level was then about 4 to 6m higher than present but exactly which ice sheets (Greenland vs. Antarctica) provided this extra water and in what proportion is unclear. The last word on the subject was probably from two papers in Science last year, which suggested that it was roughly half/half with 2m or so from Greenland, and the rest presumably from Antarctica.

Those studies had used as a data point the fact that the Dye 3 core did not appear to have any Eemian ice (unlike ice cores further north), and the minimum Greenland contribution came from a calculation of the minimum amount of ice Greenland would have to lose in order to deglaciate Dye 3. The new data in this weeks paper implies that at least some ice there appears to predate the Eemian (although the dating is uncertain enough so that it can’t be absolutely ruled out), thus the maximum Greenland contribution is likely slightly less than the numbers reported earlier. (Note that all of these estimates are based on ice sheet models, that as we have noted previously, do not fully incorporate all the physics thought to be important).

The University of Copenhagen also issued a release which expanded on the ‘stability’ issue. One of the sections is entitled “Climate theories overturned” and apparently refers to the theory that the whole Greenland ice sheet will melt as a result of global warming. This is a very odd statement indeed and doesn’t accord with any serious discussion of the issue. The authors of the press release must have received some feedback along those lines themselves, because there is an addenda added at the end that gives a bit more context:

The scientists do not want to put into question the rise in sea level during a global warming. During the last interglacial period 125.000 years ago, temperatures in Greenland were 5 degrees higher and global sea level was 4-5 meters higher than it is today. However, since the new scientific results show that the ice sheet also covered southern Greenland, the melting of the Greenlandic ice cap can only have caused a sea level rise of about 2 meters. Therefore some of the ice contributing to the sea level rise must have come from other sources, for instance the Antarctic. Furthermore, thermal warming of the oceans will cause expansion of the sea water and result in a sea level rise of half a meter, and the melting of small glaciers around the globe will result in an additional half meter rise.

This is very similar to the discussion of Eemian sea levels seen in the IPCC report, and so it is very unclear to what extent these new results ‘overturn climate theories’. And of course, the central finding – that southern Greenland was indeed deglaciated at some point in the last half million years – implies that Greenland is indeed unstable – though with a sensitivity that is still uncertain.

So we have, yet again, good science giving rise to bad press coverage, and yet again, it is unfortunately the scientists themselves that appear to have engendered the confusion.

235 Responses to “Making sense of Greenland’s ice”

Great site. Most interesting. I have a number of questions, though, that I haven’t yet found a decent answer to. As a scientist who deals with the output of biological systems I’m very much aware that data quality is absolutely critical if you are to generate good models especially in multifactorial systems. Therefore the use of ice cores as a reference database has always made me a little nervous. Part of that may or course be my own ignorance. So, perhaps you could answer a few questions. Firstly, whilst diffusion rates of gases in solids are pretty slow they are not insignificant especially when judged over large timescales. These ice cores are not single crystal lattices so I’d expect gas diffusion to be nightmare as there are so many propogation paths within various crystals and their boundaries. Given that there are also pressure changes over the length of ice cores, do you have to correct for both compression changes once the core is removed and also changing gas diffusion properties that you see at pressure? Have any of these effects been seen or measured? There are a number of other factors which I might raise but I’m curious to know if the gas diffusion effect has been observed at all. Thanks in advance. Keep up the good work, difficult as it may be.

Hank [edited] putting words into my mouth that I did not say. What I pointed out is that the sea level in the arctic is falling, which is even addressed on this site, so yes it is happening.

The change in sea level is not homogeneous, but rather the mean of the global sea level change. There are many papers on this but Jevrejeva, et al (2005) says:

The major contributions to the global sea level rise during 1920â��1940 are from the northwestern Atlantic (4.2 Â± 1.0 mm/yr), Indian (3.5 Â± 1.0 mm/yr), and Mediterranean (3.1 Â± 1.0 mm/yr) regions.

I could have used others but the generally present graphics and this was easier to point to. [edited] What I asked was since the tide gage and satellites give different answers, and it appears that the rate of change from the satellites is fairly static, then why did the rate of change from the tide gages get appended to the satellite data to correct it.

I also pointed out other peer reviewed papers that show that tide gages are not a good way to measure sea level change.

What I believe is that no one has answered my question [edited]

As for your quote, I could be wrong but I would think that melting sea ice from both the Arctic and the Antarctic could account for a significant amount of fresh water being added. But that would raise sea levels, however, the Arctic sea level is dropping.

“This is something like decadal variability. Sea level goes up and down, up and down – but in general, it rises,” the principal investigator from project explained.

“In order to make any conclusions it’s necessary to have long-term time series. We need much more data, and that’s why we will have this International Polar Year. When we combine satellites, submarines, drifting buoys, and tide gauges to get more dense data, we will be able to answer these questions.”http://news.bbc.co.uk/2/hi/science/nature/5076322.stm

Vernon, did you read the full paper you refer to?
The bit you quoted is the bit that you’d find at CO2Science, if you found it there, but you should read the whole paper.

In the full paper their next sentence is:

“… Even smoothed by the 30 year SSA window, the trends from the different ocean regions show slightly dissimilar patterns and still demonstrate some cyclic variability. This cyclicity is associated with longer term oceanic variations, changes in thermal expansion and water mass adding to the ocean, which may provide non uniform regional sea level rise, and melting of continental ice leads to the significant geographic variations in the sea level change due to both gravitational and loading effects….”

In their Abstract, they write:

“We remove 2-30 year quasi-periodic oscillations and determine the nonlinear long-term trends for 12 large ocean regions. In contrast with linear trends, where the rate of mean sea level rise is constant, our results reveal the evolution of sea level rise during the 20 century and show that the highest regional rates of up to 3-5 mm/yr occurred between 1920-1950 (with some regional variations). Our global sea level trend estimate of 2.4 mm/yr for the period from 1993 to 2000 is comparable with the 2.6 mm/yr sea level rise calculated from TOPEX/Poseidon altimeter measurements….”

No surprise there. The warming signal in the oceans isn’t new. The worry is how long it will go on and what Greenland’s melting, among other land sources, will add to it. For example:

http://www.nersc.gov/news/annual_reports/annrep05/assets/img/research_news/01-heat_clip_image002.jpg
“The half-degree temperature rise is similar to that observed during the second half of the 20th century, but the projected sea level rise is more than twice the 5-centimeter (2-inch) rise that occurred during that period. These numbers do not take into account fresh water from melting ice sheets and glaciers, which could at least double the sea level rise caused by thermal expansion alone…. 100 years after stabilization in the study, ocean waters continue to warm and expand, causing global sea level to rise unabated (Figure 1).”

Small connections? IIRC the Bering Strait is about 50 miles wide, the Baffin Strait several hundred. Then there’s the gap between Greenland & Europe, with only Iceland in it.

Well, it isn’t just the width of the connections, but the depth. Both straits are for the most part more shallow than the Arctic Ocean, I would presume – particularly its central basins.

I just don’t see how, absent significant changes in wind patterns or currents, you could get different sea levels in different places.

It does seem rather strange, doesn’t it?

But there is the Southern Oscillation, the Pacific Decadal Oscillation and the Arctic Oscillation, all of which are due to the interaction between the atmosphere and the ocean. Over large enough areas the interaction between the atmosphere (principally due to air pressure) and the ocean (e.g., water flow, temperature and salinity) is sufficiently strong to produce millimeters of rise and fall over time. In terms of the general principles, this sort of phenomena is fairly well understood, but the arctic is a little more remote – so we know less regarding its specifics at this point.

Jim, that John Daly page you refer people to is a decade old — from the Greening Earth Society.

You might point to what’s been learned in the last ten years for updates.

“… Few effects from global warming raise more red flags than rising sea levels. The topic has led to a growing pile of conflicting research trying to answer the questions: How fast, and why?

“Now, a pair of US scientists conclude that the oceans rose at a global average rate of 1.5 to 2 millimeters a year (6 to 8 inches a century), confirming a hotly debated, decade-old estimate. But their work also points to the key driver of this change: water from melting glaciers and not, as some have argued, a natural swelling of the oceans caused by higher temperatures. …”http://www.csmonitor.com/2004/0325/p17s02-sten.html (2004)

“Ice melt from small glaciers and ice caps will be the dominant cause of sea-level rise this century, according to new research. Scientists have previously suggested that the ice sheets of Antarctica and Greenland would be most responsible for rises as the Earth warms, as they hold the overwhelming majority of the world’s frozen water.

Hank, read 163 where I first made the cite that satellite reading are modified by the tide gage trends to make the satellite readings more “accurate”.

[edit]

Please quit attributing where I get my cites from when I give you the cite. All your trying to do is make me out a denialist. I am a skeptic and have been presenting the things that make me skeptical, so please discuss the science and quit trying to paint me as something I am not.

Re #205: [Do you know how deep the ocean is on either side of those connections, and how deep the basins are on either side?]

Why should it matter how deep the basins are? This is liquid we’re talking about: it should spill over the edge of the basin, no?

Please understand that I’m well aware of things like tides, variations due to winds and atmospheric pressure changes, and so forth. Let’s lump those all together and label them “sloshing around”. So after you account for all the sloshing around, how do you get long-term sea level varying from one place to another?

That’s OK, and in fact helpful — that Daly page _does_ talk about how they set up a network of island-based tide gauges, back when the satellite system was rolled out — and says they were using the tide gauges along with the first satellite results to figure out what they were getting.

Perhaps the questions about using tide gauges to correct satellite results arise from reading that page about the early days. Just guessing of course.

It’s not just “liquid” — it’s a heat engine, the biggest one we have handy to study — multiple and changing variables, on a rotating and uneven sphere, in a varying gravity field, on an uneven bottom, interacting through vapor and ice transitions as well.

[[In light of the discussion about sea levels i’ve recently come across a couple of mentions re Dr Nils Axel Morner from Sweden. He apparently withdrew from IPCC – here’s a taster of what he claims “paleogeophysicist Nils-Axel MÃ?Â¶rner, whoÃ¢??s been studying and writing about sea levels for four decades, the scientists working for the IPCC have falsified data and destroyed evidence to incorrectly prove their point”. ]]

First of all, kudos to Hank for correctly writing “gauges” instead of “gages.”

Sea level does, in fact, differ all over the world. Gravity is not the same from place to place and neither are currents, and both affect local sea level. Water flows, but that’s not the only factor involved.

In addition to the factors mentioned by Hank and Barton, atmospheric pressure also affect sea level (a very localized example is the low pressure inside a hurricane that sucks up a mound of water that, when it reaches shore, esp. at high tide, creates a destructive storm surge).
For a technical explanation of regional differences in sea level, see Chapter XIII, pages 458-469, and Chapter XV in The Oceans, by Sverdrup, Johnson, and Fleming ( http://ark.cdlib.org/ark:/13030/kt167nb66r ).

That’s what I’d been thinking…..what about all the other glaciers? I mean, if the warming is global…..

But apparently they won’t amount to nearly as much sea rise as Antarctia or Greenland, once these get into serious melting — only about one foot (that also sounds like a low estimate for near complete melting of ALL other glaciers and snow packs of the world once it gets really hot enough to do that).

So, given a high end BAU scenario and a warming of 5C by 2100-2200, and all sorts of positive feedbacks kicking in, when would all this glacier melt & sea expansion cause the sea to rise by, say, 20 meters, 60 meters, 100 meters? Might it be in 200 or 500 years (under a worse-case BAU scenario)?

The article said we didn’t have to worry much this century, but that’s a cop-out. I’m concerned about the total extent of this warming, caused and/or triggered by our industrial soc GHG emissions, whether it goes on for 100 or 1,000 or 10,000 or 100,000 years. It’s about moral responsibility, not about getting some water in my house (which I did get in these recent S. TX floods).

But gravity in a sense defines “level”, doesn’t it? You’ve got the Earth, and if you take all the local variations in gravity, the centrifugal force from its rotation, the influence of lunar & solar gravity, and so on, you have a not-quite-spherical equipotential surface to use as a reference. If you didn’t have all that weather stuff, the sloshing, going on, liquid ought to follow that surface, no?

(And yes, that surface is variable, as the positions of moon & sun change, and the liquid follows that changing surface, but the average stays the same.)

[…and neither are currents, and both affect local sea level.]

OK, now add in the sloshing. A current might raise the level here, depress it there, and the same for weather systems. But those are either going to be consistent, or they’re going to vary about some median value. If you have a gauge at some point, and filter out the sloshing so you just see long-term trends, you shouldn’t see a change unless there is a causative change in currents or weather. (Ignoring glacial melting &c for now.)

So if Arctic sea levels are indeed decreasing, instead of the surrounding land rising due to glacial rebound, what’s the cause?

Agreed in general, and certainly the air pressure changes affect sea level variations in the Arctic Ocean. There’s a lot of published science on this. Just one example:

“This study examines high-frequency sea level variabilities induced by surface pressure loading comparing with surface wind stress….
In the Arctic Ocean, pressure induced component reaches more than 90 % of the variability forced both by pressure and wind. …. The average sea level delays since the basin-wide isostatic adjustment is only established by the limited water exchange through the strait. …..”http://www.agu.org/cgi-bin/wais?ee=OS25Q-01

Note that Sverdrup et al. was published about 1942. They wrote “equatorial and polar radii are given in table 2, with other data concerning the size of the earth that can be computed from these values. The values for the equatorial and polar radii are those for sea level….. In the open ocean the deviations from the ideal sea level rarely exceed 1 or 2 m. The errors that are introduced by referring soundings to the actual sea surface are insignificant in deep water, where the errors of measurement are many times greater. …” That’s clearly wrong, as we know from the satellite work — the planet’s far lumpier than had been thought!

I saw this quote in Science Daily talking about glacial melting “While this is a dynamic, complex process and does not seem to be a direct result of climate warming, it is likely that climate acts as a trigger to set off this dramatic response,” said U-Boulder geology Professor Robert Anderson, study co-author. Also INSTAAR researcher. http://www.sciencedaily.com/releases/2007/07/070719143502.htm

The IPCC Working Group One – “Physical Basis for Climate Change” thought glacial melt was caused by climate climate change. What gives?

Jeanette, read that again, I think you misread the antecedent for the word “this” as meaning “glacial melting” but
as I read it, his “this” refers to the stretching and sliding of the ice — the rate at which it moves, how much of it is supported by water, so how much it calves. That’s clearly not a “direct result” of “global warming” — you can chart the global temperature change and compare it to the rate of different glaciers and ice caps and they vary, so it has to be an _indirect_ relationship.

What’s “direct” is probably something like water melting on the surface. By the time that gets to the base, and gets translated into movement, a lot of other variables have been involved. See if you read it that way. If we’re lucky, maybe he or one of the researchers involved can tell us what the meaning is supposed to be.

———-excerpt——–

“Water controls how rapidly glaciers slide along their beds, said Anderson. When a glacier with its “toe in the water” thins, a larger fraction of its weight is supported by water and it slides faster and calves more ice into the ocean at the glacier terminus.

“While this is a dynamic, complex process and does not seem to be a direct result of climate warming, it is likely that climate acts as a trigger to set off this dramatic response,” said Anderson.

—– end excerpt ——

So I’d say “this” dynamic complex process — how rapidly glaciers slide — is what’s triggered by climate. Look at the icequake rates and numbers in Greenland and Antarctica.

I saw this quote in Science Daily talking about glacial melting “While this is a dynamic, complex process and does not seem to be a direct result of climate warming, it is likely that climate acts as a trigger to set off this dramatic response,” said U-Boulder geology Professor Robert Anderson, study co-author. Also INSTAAR researcher. http://www.sciencedaily.com/releases/2007/07/070719143502.htm

The IPCC Working Group One – “Physical Basis for Climate Change” thought glacial melt was caused by climate climate change. What gives?

I would presume that they mean that in the case of each glacier, the process is complex involving numerous factors, including the unique history and geological setting of the glacier, where the history will include the specific weather that it has been subject to. In essence, this is the same principle behind not trying to attribute any given storm, flood, drought or hot summer day to global warming. As he and many others view it, global warming isn’t a particular entity like a storm, flood or drought. As such it cannot cause these things. Global warming, or rather climate change, is something more statistical in nature – which makes these sorts of things more probable.

In the same way, you can’t speak of “human” as walking along the street, being a certain height or having a particular hair color, but you can speak of a particular human doing, being and having these things.

Re: Timothy Chase, Climate change is a gradual process that adds to the effects of natural climate variablity. Therefore in a way they are right for saying there is no ‘direct link’. Only over time can the big picture be fully appeciated by the dramatic rise in hurricane numbers and their intensity over the last 20 years..fact! The number of tornadoes and their intensity over 20yrs..fact!. The number of temp records broken all over the world..either high or low..fact! And photographic evidence of glacial melt in europe, the americas, greenland..etc..etc..fact! Each of these taken and analysed alone is insufficient evidence for drawing a direct correlation to climate change..but all these signs and climatic conditions taken together do indeed draw a very direct connection to climate change. Even blind Freddy would see the connection. I now understand why climatologists prefer the term ‘climate change’ over ‘greenhouse effect’, for the reason that it effects every part of the world differently. But what is true all over the world is that virtually every country’s usual weather patterns ate becomming very unstable and unpredicable. Cold snaps even more intense..heat waves last longer and are more severe. Thunderstorms are far more vicious and damaging, rain periods now cause widespead flooding far more regulary than in the past. Here in sunny queensland australia..after our hottest autumn on record..we are now having our coldest winter on record..many many records have been broken for extreme cold. This has caused one of our worst influensa outbreaks for decades.

James, oscillations? That doesn’t mean they’re like sine waves or clockwork, that means things that vary, and how they vary is part of what’s being studied. You read about the Arctic Oscillation, right?

> If you have a gauge at some point, and filter out the sloshing so you just see long-term trends
But “if” isn’t a data set — what gauge would you look at? The ones in the record?

The ones referred to in previous postings are mostly along the coastline of Russia.

If you read the studies already cited and followed the links you know as much as has been published.

Did you read Proshutinsky et al.? Note the dates

“… sea level change is the net result of many individual effects of environmental forcing. Since some of these effects may offset
others, the cause of the sea level response to climate change remains somewhat uncertain. This paper is focused on an attempt to provide first-order answers to two questions, namely, what is the rate of sea level change in the Arctic Ocean, and furthermore, what is the role of each of the individual contributing factors to observed Arctic Ocean sea level change? In seeking answers to these questions we have discovered that during the period 1954 – ­1989 the observed sea level over the Russian sector of the Arctic Ocean is rising …. There are two major causes of this rise. The first is associated with the steric effect of ocean expansion…. The second most important factor is related to the ongoing decrease of sea level atmospheric pressure over the Arctic Ocean… A third contribution to the sea level increase involves wind action and the increase of cyclonic winds over the Arctic Ocean …. The combined effect of the sea level rise due to an increase of river runoff and the sea level fall due to a negative trend in precipitation minus evaporation over the ocean is close to 0…..”

Got that? Now, look back at the Arctic Oscillation graph you made —— look at it with the 120-month average. Look like it fits?
Maybe. Just guessing here. You can probably do better, if you have the time to study it.

Re: Timothy Chase, Climate change is a gradual process that adds to the effects of natural climate variablity. Therefore in a way they are right for saying there is no ‘direct link’. Only over time can the big picture be fully appeciated by the dramatic rise in hurricane numbers and their intensity over the last 20 years..fact!…

I wasn’t agreeing or disagreeing.

In fact, given the logic of what I stated it seems unavoidable. But I was stating it without stating that it is something that I agree with or disagree with – because I can understand the frustration someone might experience over not being able to say that, “Global warming is the cause of the decline of our glaciers,” direct or not. Additionally, one can argue in any particular case in which one can distinguish between cause and effect that the cause is not “the cause of the effect” but merely contributes to it. In a sense, this is true – but largely philosophical in nature. People ordinarily don’t think like that – and will omit various factors from their analysis. At a certain level, we have to simply in order to be able to act in the world.

However, thank you for bringing up the gradual nature of the process. It makes the original argument stronger.

Re 228: Lawrence, how is the water situation in the Murray-Darling basin? The new favorite “expert” of the contrarian camp, 15 yr old Kirsten Byrnes had predicted its end and I read somewhere that farmers have planted a lot of crops in anticipation of winter rains. However, it seems that the prime minister has already mentioned the possibility of shutting off all irrigation to preserve drinking water.

Can anyone explain how the air pressure over the Arctic sea is dropping (which should raise sea levels) yet the sea levels in the Arctic sea are actually dropping?

This does imply that the actually amount that the sea levels are dropping would be greater than actually measured.

This lead me to start looking for correlations between barometric readings and measured sea levels. I ask this because barometric pressure will affect sea levels and I was wondering how this was adjusted for. I saw with satellite readings they adjust for travel time due but not where they adjust the measured sea level based on the perceived air density. With tide gauges I would expect it to be worse historically.

So does anyone know where to find a paper that shows the correlation between apparent sea level measurements and actual in reference to barometric pressure?

Unfortunately only a relatively small part of the available Arctic ocean weather and climate data is unclassified (that from the so-called “Gore Box”– Al Gore got the Navy to declassify an area back when he was vice president).

Most of the work that’s come out of that can be found searching for thesis papers at the Navy’s post-graduate school website (Monterey CA). I’ve pointed to it previously, but they do keep rearranging their pages so none of the old links work. Searching will find it.

Other than that, there are compliations, searching comes up with some:

Meanwhile, back ON topic — I just finished Ward’s “Under a Green Sky” and take his point that what’s correlated with previous great extinction events was not a halt of the deep ocean transport but rather a rearrangement of it to where it carries warmer, less oxygenated water into the deep, leading to anoxic conditions. He does make his point clear that he’s more or less shouting across the gap between paleontology (focused on deep time) and climatology (focused on since-the-last-glaciation) and flagging for the climatologists the concern that the deep ocean circulation can simply move a bit sideways and cause a very profound change in oxygenation of the deep. He notes the lag between writing and publication, and doesn’t have the latest news about melting of small high glaciers’ contribution — which puts fresh water into a different area than melting of Greenland. I hope he’s reading this and can comment more.